Variations in well profile exist according to vertical, slant, directional and horizontal trajectories. Measurement may involve the acquisition and communication to surface of various types of wellbore data such as resistivity, porosity, permeability, azimuth, inclination and borehole diameter or rugosity, formation dips or bedding angles.
Previously, the underreamer and bit have been considered as separate tools, each involved in distinct functions. Typically, underreaming can involve several runs to achieve the desired wellbore diameter, after the bit has drilled the section. The time-lag between underreaming and drilling, therefore could easily exceed 48 hours depending on the depths involved. If the actual hole diameter did not match the planned diameter, casing tolerances would not be met and therefore a corrective run would be required and the whole cycle of underreaming would need to be repeated.
In the aspects of cutter element placement and nozzle location the present invention is differentiated from and shows advantages over the prior art. A major drawback of prior art underreamers is their cutting performance in terms of maintaining similar rates of penetration to the bit. To one skilled in the art, it is known that the bit has optimized cutter element placements and nozzle locations, and this often leads to the bit outperforming the underreamer. Consequently, this leads to either a separate underreaming run after drilling the section, or leads to the underreaming-while-drilling itself taking several attempts before a complete section is underreamed satisfactorily.
In terms of drilling dynamics, the optimised drill-bit drills at a faster rate of penetration than the underreamer which has trouble maintaining similar rates of penetration. Due to the distances between the bit and underreamer which may be 120 ft (36 m) or more, the bit may have exited a hard formation or layer while the underreamer may just be entering the earlier hard formation or hard layer as it is may not be connected directly to the bit. The prior art underreamers have limited cutter elements in contact with the wellbore and limited nozzle cleaning action due to the location of nozzles outside the cutter block elements.
Further the prior art generates time-consuming cycles of entry and exit into the well-bore.
Further the prior art has limited cutter elements in contact with the wellbore.
Further the prior art has limited practical application of a mechanical caliper outside the cutter block.
To those skilled in the art, it is known that the industry relies on even more rudimentary and time-consuming indicators of verification such as an increase in drilling torque as cutters interact with the formation or even pulling up the drill-string and underreamer to the previous hole size in order to see whether the top-drive stalls as the bottom-hole assembly gets stuck due to the expanded tool.